A prior art magnetic tape has been manufactured by coating a polyester film or like substrate with a magnetic material, e.g., ferrite particles, together with a solvent and, after drying, pressing the coating by calendar rollers. This magnetic tape is referred to as a coating type magnetic recording medium. When this coating type magnetic recording-medium uses a polyester film as a substrate, a substrate having as small a thickness as possible is selected to permit long use. To improve friction, thereby providing for a satisfactory running property (or slipping property), the film substrate is formed with fine surface irregularities by producing internal particles during manufacture of the polyester or by externally adding fine particles of silica or the like.
Recent research has focused on magnetic recording media which comprise a non-magnetic support provided with a ferromagnetic thin metal film formed thereon by plating, spattering, vacuum deposition, ion plating, etc. as high density magnetic recording media to replace conventional coating type magnetic recording media.
However, the magnetic recording media provided with ferromagnetic thin metal films formed in the above processes, have problems in near resistance and running. During the recording and reproduction of a magnetic signal, a magnetic recording medium is moved at high speed relative to a magnetic head or guide. The magnetic recording medium should run smoothly and stably. The ferromagnetic thin metal film which is produced by any of the above processes, however, can not withstand stringent conditions during the magnetic recording and reproduction. That is, it becomes unstable due to friction with the magnetic head. In addition, when it is driven for a long time, it may become worn or broken, or its output may be reduced due to generation of particles produced by wear. Accordingly, it has been proposed to form a monomolecular film of a saturated fatty acid or a metal salt thereof on the ferromagnetic thin metal film (Japan Tokkai Sho 50-75001/1975).
However, if fine surface irregularities formed on the film surface include even very slight projecting portions, such portions can be transferred to the recording medium which is in contact with the film when the film is wound on it. In this situation, recording may no longer be possible, and breakage may result.
In many of the high density magnetic recording media, the initial lubricating property may be slightly improved by adopting such means as disclosed in Japan Tokkai Sho 50-75001/1975. However, slip durability is lacking, and the running stability and wear resistance are undesirable. This is attributable to a weak physical adsorption between the unsaturated fatty acid monomolecular film and the ferromagnetic thin metal film as well as to the consequent scraping-off of unsaturated fatty acid by the magnetic head which is in frictional contact with the running recording medium.
Lubricants for magnetic recording media will now be considered.
As conventional lubricants, there are solid and liquid lubricants. Solid lubricants have become obsolete because it is difficult to coat them uniformly. Liquid lubricants are used to form lubricant films by spin coating or dipping. However, they are coated to thicknesses of at least 50 angstroms. Therefore, limitations are imposed when films are disposed closer to magnetic heads as a result of increasing the density and capacity of the films. Besides, lubricants are readily collected in depressed portions of the fine surface irregularities in the magnetic recording medium. Lubricants are scarcely found on raised portions of the surface, the wear of which is due to contact between the head and magnetic recording medium. Moreover, it is difficult to accurately control the amount of lubricant when applied as it many spatter if applied excessively. Therefore, requirements for the lubricant film have not been met.